When drilling, a coring tool may be used to obtain a core sample of the formation being drilled. This generally involves a coring bit that is open in the center, and a barrel behind the coring bit. The barrel receives and holds the core sample as it enters through the center of the coring bit.
Often, the barrel and the related components will be made from a different material than the coring bit and the drill string that drives the coring bit. As a result, differences in the coefficient of thermal expansion between materials can change the relative position of the coring bit and the barrel when exposed to different temperatures. While coring tools are generally designed to account for this, the temperature in any particular well may be different from the design.